1. Field of the Invention
The present invention relates, generally, to a die-casting apparatus and, more specifically, to a die-casting apparatus having mechanically actuated bank core slide assemblies to produce die-cast engine blocks.
2. Description of the Related Art
Die-casting is widely used in the manufacture of component parts in the automotive industry. Die-casting can provide component parts having complex shapes and surfaces with a high degree of accuracy, which reduces the need for additional machining steps. Furthermore, the accuracy of die-casting provides highly repeatable production processes that can be automated to provide labor cost savings and speed. One notable application of automated die-casting processes in the automotive industry is the die-cast forming of engine blocks. Engine blocks have extensive and complex surfaces with close tolerances and producing them by die-casting permits rapid and accurate production that eliminates a number of costly machining operations and saves time and material. However, die-casting of engine blocks requires that the die-casting dies, or apparatuses form an accurate die cavity that must be capable of withstanding not only the high temperature of the molten metal, but also the extreme pressures applied to the molten metal to force it into the smallest portions of the die cavity.
To form the die cavity necessary to produce an engine block, conventional die-casting dies are fitted with a number of die elements and die cores that operatively cooperate with each other. The majority of die elements and cores are movable with respect to a single stationary element such that the movable elements are closed about the stationary element to form the die cavity and are retracted from the stationary element to open and allow extraction of the cast engine block. Generally, conventional die-cast dies have a stationary element, two movable side elements, and several slidable elements that provide cores to form the cylinder bores when the engine block is cast. Due to their large and heavy nature, conventional die-casting dies hydraulically drive the movable elements and the slide elements between their open and closed positions. When driven to the closed position, the alignment and the placement of the cylinder cores within the die cavity are critical as misalignment can vary wall thicknesses and distort surface dimensions to unacceptable limits and result in a substantial waste of die-cast parts.
Conventional die-casting dies have generally been able to adequately deal with difficulties in producing engine blocks. However, there is still room for improvement in the design of these devices that would allow for greater efficiency and cost savings. This is especially true as the die-casting process applies to the production of engine blocks having a “V” cylinder configuration. In particular, the die-casting of a “V” type engine block requires a pair of cylinder-forming, die core slide elements that are positioned within the die cavity at an offset angle to each other. Each of the core slides include a plurality of core inserts that form the cylinder bores within the engine block casting. Thus, the core inserts of the two core slide form two “banks” of cylinder bores within the engine block. These “bank” core slides are movably mounted within a portion of the die-casting dies generally known as the ejector holder so that they can be extended into the die cavity for the casting process and extracted to release the cast engine block.
The ejector holder is one of the movable elements of the die-casting dies, which is driven toward the stationary element to close the die-cavity. Two opposing side core slides are actuated to move perpendicular to the ejector holder and provide the side molding surfaces of the die cavity with respect to the stationary element and the ejector holder. The side core slides, the ejector holder, and the bank core slide assemblies are moved against the stationary element and locked in place to close the die cavity.
When die-casting an engine block, properly locking the bank core slide assemblies and accurately retaining them in the desired position to maintain the dimensional stability of the bank core slides, and thus the cast cylinder bores is somewhat problematic. The dimensional instabilities of the bank core slide assemblies are most often compensated for by casting thicker cylinder walls and performing additional machining steps. However, this is not a cost effective solution and not only increases the costs of materials but also increases the time and labor costs in producing a usable engine block. Accordingly, there remains a need in the related art for an engine block die-casting apparatus that ensures an accurate and highly repeatable placement of the bank core slide assemblies in the die cavity such that dimensional stability is ensured.
Additionally, forming of the cylinder walls in a die-cast engine block places a great deal of formed metal about the core inserts of the bank core slides. The quantity of metal in the formed cylinder walls about the core inserts is necessary to provide the proper strength and integrity to the cast block. However, the solidified cast metal tends to hold the core inserts and the bank core slide assemblies in place and makes extraction of the core inserts from the formed cylinder bores difficult. Thus, conventional die-casting dies utilize large hydraulic actuating assemblies to provide the force necessary to extract the core inserts from the cast engine block. These large hydraulic actuating assemblies require high hydraulic pressures to overcome the hold of the cast metal on each of the core inserts. Furthermore, due to the length of the stroke necessary to extract the cores inserts from the cast engine block and their sheer physical size, the hydraulic actuating assemblies must be located outside of the ejector holder block and back from the bank core slides. This necessitates further complexity in connecting the bank core slide assemblies to the externally mounted hydraulic actuating assemblies. Accordingly, there remains a need in the related art for an engine block die-casting apparatus that eliminates the large and complex hydraulic actuating assemblies for moving the bank core slide assemblies as found in conventional die-casting machines and that employs a simplified and compact bank core slide actuation system.
In addition to these issues, as in all die-casting processes, some small quantities of the extra molten casting material escapes from, or is forced into the areas where the die elements join. As this extra material solidifies, it forms waste casting debris. In the die-casting of engine blocks, the debris, or “flashing” must be cleaned from the die elements and the core inserts of the die-casting machine before the next casting event. Any flashing that remains attached to, or between, the die elements and core inserts of the die-casting dies will interfere with the next die-casting process and may damage subsequent castings if it is not removed after each casting extraction. Conventional die-casting dies are generally not capable of self-cleaning or clearing the flashing so that human intervention is required to ensure that the die elements and cores are clear of flashing and debris after each casting event. This is a time consuming and difficult procedure to perform in the tight, highly heated confines of an engine block die-casting machine. Accordingly, there remains a need in the related art for an engine block die-casting apparatus that provides a means for automated clearing of the flash and debris formed during the casting process.
Furthermore, conventional die-casting dies fail to address the dissipation of the heat inherent in the die-casting process. This disregard of the heat from the casting process negatively affects the maintenance and repair costs. More specifically, the heat of the molten metal when injected into the die cavity and the dissipating heat of the metal as it forms into an engine block is transferred into the die elements and core inserts of the die-casting machine. The conventional bank core slide assemblies and core inserts for the die-casting of engine blocks are not operatively cooled when extracted from the cast engine block and are merely recycled to the closed position for the next casting process. This affects the dimensional stability of the core inserts. As the core inserts are exposed to the cooler ambient air and before they are recycled back into the closed die, the heat dissipates unevenly from the core inserts and the bank core slides. This uneven dissipation introduces temperature differences and subsequent dimensional differences or instabilities between the core inserts of the two bank core slide assemblies and between the individual core inserts of each bank, which may cause unacceptable dimensional variations.
In addition, the core slides become heat stressed such that their metallurgical properties change causing them to wear rapidly in their interaction with the formed castings. This rapid wearing of the core inserts requires that they be replaced often, which greatly adds to the maintenance costs and down time of the die-casting dies. Accordingly, there remains a need in the related art for an engine block die-casting apparatus that provides a means for operatively cooling the core inserts in each of the banks between the casting cycles.